The separation of components of gas mixtures is of considerable industrial importance. When the separation is conducted on a large scale, fractional distillation is often employed. However, distillation is quite expensive because of the large initial capital cost of distillation equipment and the considerable energy required for the operation of such equipment. In recent times other separation methods have been investigated in efforts to reduce the overall cost of gas separations.
A gas separation technique that has been used as an alternative to distillation is adsorption. In early work in this field, Milton, in U.S. Pat. Nos. 2,882,243 and 2,882,244, described the preparation of novel crystalline aluminosilicates, which he called type A and type X zeolites, and the use of these materials to separate components of gas mixtures such as air. In U.S. Pat. No. 2,882,243, Milton described the preparation of zeolites having particle sizes in the range of 0.1 to 10 .mu.m (microns). Milton used his new zeolites with some success for the adsorptive separation of nitrogen from oxygen.
Other workers in the field recognized the importance of using zeolites having small and uniformly sized crystals as adsorbents for gas separation processes. Robertson, in U.S. Pat. No. 4,173,622, described the production of zeolite A adsorbent having a particle size in the range of 1 to 10 microns. He prepared his adsorbent by seeding a sodium aluminum silicate using adsorbent nucleating particles having an average size less than about 0.5 micron. Similarly, Strack et al., in U.S. Pat. No. 4,303,629, described the production of type A zeolite in which 50% by weight of the particles have a maximum size of 4 microns. Kostinko, in U.S. Pat. No. 4,443,422, described the preparation of zeolite A having an average particle size of less than 1.7 microns and zeolite X having an average particle size of less than 2.2 microns. This patent gives a detailed summary of the patent literature in the field of zeolite preparation.
Small particle size adsorbent is difficult to use in cyclic adsorption processes because of the tendency of the fine particles to cake and consequently increase the pressure drop across a bed of such adsorbent. Small particle size material also has a tendency to fluidize and pass through screen material in the adsorption equipment. For this reason, zeolite crystals are formed into shaped particles, such as pellets, beads, etc., of macroscopic size, i. e., millimeter range size.
The rate of transport of adsorbed components of gas mixtures into adsorbents has been determined to be an important factor in the efficiency of adsorption processes. Research efforts are continually made to find ways to increase the rate of infusion and effusion of sorbed components into and out of adsorbent particles during the various steps of cyclic adsorption processes. The present invention presents new adsorbent products that accomplish this objective.